Potentiometers

ABSTRACT

Potentiometers having a reduced number of parts and an improved wiper design suitable for manufacture in a miniaturized form. The resistance element is a conductive film disposed in a circular arc on a ceramic substrate. The substrate also has a conductive pad disposed concentrically with respect to the resistive element and terminal connections are made for each end of the resistive element and to the central pad. A drive member is disposed coaxially with the resistive element and a wiper member is disposed therebetween so as to be driven in rotation by the drive member and to be elastically encouraged into contact with both the central contact area and to the resistive element through a plurality of wiper contacts. A single turn model having a positive stop and two multiple turn models having a clutching means driving the wiper member are disclosed.

United States Patent Hamill [54] POTENTIOMETERS [72] lnventor: Arthur L. Hamill, Los Angeles,

Calif.

[73] Assignee: Techo-Components C0rp., Van

Nuys, Calif.

[22] Filed: Feb. 22, 1971 21 Appl. No.: 117,500

[52] US. Cl ..338/l62, 338/DlG. l [51] Int. Cl. ..ll0lc 9/02 [58] Field of Search ..338/DlG. l, 174, 180, 162

[56] References Cited UNITED STATES PATENTS 1 Aug. 8, 1972 Primary ExaminerLewis H. Myers Assistant Examiner-D. A. Tone Attorney-Spensley, Horn & Lubitz [57] ABSTRACT Potentiometers having a reduced number of parts and an improved wiper design suitable for manufacture in a miniaturized form. The resistance element is a conductive film disposed in a circular are on a ceramic substrate. The substrate also has a conductive pad disposed concentrically with respect to the resistive element and terminal connections are made for each end of the resistive element and to the central pad. A drive member is disposed coaxially with the resistive element and a wiper member is disposed therebetween so as to be driven in rotation by the drive member and to be elastically encouraged into contact with both the central contact area and to the resistive element through a plurality of wiper contacts. A single turn model having a positive stop and two multiple turn models having a clutching means driving the wiper member are disclosed.

8 Claims, 9 Drawing Figures PAIENTEDAuc 8 I972 SHEET 1 OF 2 as 42 40 a2 INVENTOR 1 7 f GPA/,5 y g PATENTEDAuc' 8 I972 3.683; 308

' I NVEN TOR.

29 H2 '06 1 BY BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention relates to the field of potentiometers.

2. Prior Art.

Very rapid advances have been made over the last few years in both passive and active components for use in electronic circuits. Semiconductor devices and particularly integrated circuits which only a very few years ago were not available or were too costly for general use are now available in such varieties and at such prices as to make them attractive for use in most applications. By way of example, integrated direct coupled amplifiers are now available in a standard transistor package for only a few dollars or less and provide a highly reliable high gain amplifier for use in a multitide of circuits. Components such as this are used with other discrete components such as resistors, capacitors, potentiometers, etc. to fabricate the desired electronic system. Because of the small size and low cost of the semiconductor devices, a very substantial portion of both cost and size of an electronic circuit is attributable to the cost and size of the discrete components. Consequently, there has been an increasing effort to further miniaturize and to lower the cost of the discrete components because of the limitations these components now impose on the overall system. Hybrid circuits, and particularly large scale integrated circuits cause an even greater emphasis on size, cost and reliability of the discrete components.

Certain discrete components, such as resistors and capacitors, lend themselves to miniaturization. By way of example, resistive films may be deposited on a small substrate to achieve a small resistor, or a network of resistors for interconnection into a circuit. Resistors may also be formed as a part of the semiconductor device by doping a semiconductor area to achieve the desired resistivity. Capacitors may also be located on a semiconductor chip, taking the form of a back biased PN junction or as a semiconductor-oxide-metal sandwich. On the other hand, circuits are normally designed to avoid the use of inductive elements wherever possible because the size, cost and reliability of such components is inconsistant with modern circuit requirements.

Most electronic systems require provisions for adjustments thereto to adjust such things as biases, gains, voltage levels, etc. so that the desired circuit performance may be achieved without excessive control on each individual element used within the circuit. Such adjustment provisions are normally achieved by the use of potentiometers. Since potentiometers characteristically are a rather large component and tend to have a relatively low reliability, there is a great demand for miniature potentiometers having an improved reliability and lower manufacturing cost.

Miniaturized potentiometers have been manufactured for a number of years in a number of different designs, including both film potentiometers and wire wound potentiometers. Such devices have tended to have complicated designs and to involve the assembly of a great number of exceedingly small parts. The net effect is that tolerances in the parts tend to accumulate because of the number of parts involved, so as to diminish the accuracy and reliability in the finished potentiometer. Also, the assembly of a large number of small parts affords a great opportunity for human error and grossly contributes to thehigh cost of prior art potentiometers.

BRIEF SUMMARY OF THE INVENTION Potentiometers having a reduced number of parts and an improved wiper design suitable for manufacturing in a miniaturized form. The potentiometers of the present invention are film potentiometers having a circular arc of resistance film on a ceramic substrate. The substrate also contains a conductive pad concentric with the resistive element and conductive connections to the ends of the resistive element. The potentiometer enclosure is comprised of two plastic members sonically welded together during assembly. One of these plastic members contains a provision for mechanically driving a wiper. The other plastic member retains the ceramic substrate and in general supports terminals interconnected with the ends of the resistive elements and with the centrally disposed conductive pad. A wiper member of special design is elastically retained between the drive member and the ceramic substrate so as to encourage a plurality of wipers into electrical contact with the resistive film and further to provide an integral center contact with the contact pad on the substrate so as to provide a wiper connection to the wiper terminal of the potentiometer.

Various configurations of the present invention are disclosed. One configuration has a provision for direct drive through a drive member by a small screw driver or special tool for this purpose and further has the terminals extending outward through one end of the potentiometer enclosure. In this configuration, the wiper drive member is maintained in engagement with a sealing member by contact with the portion of the wiper contacting the central contact pad. A second configuration has the same terminal arrangement but has a lead screw drive through a clutching provision to provide a single turn of the wiper upon multiple rotation of the lead screw. A third configuration also has the lead screw drive but has the terminals extending through the side of the potentiometer enclosure rather than through the end of the enclosure. All configurations have positive stops for the wiper so as to limit the wiper travel to something less than one full turn, so that no wiper opens or sudden jumps in output are encountered. Interchangeable parts are used wherever possible in these configurations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a cross-section of a potentiometer of FIG. 1 taken along lines 22 of that figure.

FIG. 3a is an exploded view in perspective of the potentiometer of FIG. 1.

FIG. 3is a partial cross-section of the potentiometer of FIG. 1 taken along lines 3b-3b of FIG. 2.

FIG. 4 is a top view of base member 34 showing substrate 38 and the electrical connection to the various regions thereon.

FIG. 5 is a perspective view of the wiper of the potentiometer of the present invention such as shown in FIGS. 1,6 and 8.

FIG. 6 is a cross-section of an alternate embodiment of the presentinvention.

FIG. 7 is a perspective view of the potentiometer of FIG. 6 illustrating slot 87 in side member 85 and the terminals on the potentiometer.

FIG. 8 is a perspective view of a further alternate embodiment of the present invention, illustrating the arrangement and connection of the terminals to the various layers on substrate 38.

DETAILED DESCRIPTION OF THE INVENTION First referring to FIG. 1, a perspective view of one embodiment of the present invention may be seen. In this embodiment the provision for driving the potentiometer wiper is a lead screw and gear, the lead screw having a screw head accessible on one side of the potentiometer 22. Terminals 24, 26 and 28 extend outward through the base 34 of the potentiometer 22. Also visible in FIG. 1 is the sonically welded seam 30 joining top member 32 and base member 34.

Now referring to FIG. 2, a partial cutaway of the potentiometer of FIG. 1, taken along lines 2-2 of that figure, may be seen. Terminals 24, 26 and 28 have an enlarged head 36 which is molded into the base member 34 of the potentiometer (only terminal 26 and 28 are visible in FIG. 2.) A ceramic substrate 38 is located on the bottom of base member 34 and has a first coating comprising a conductive central contact area 40, and a resistive path 42 disposed in an are about the central pad 40. The top member 32 houses a lead screw assembly, details of which will be subsequently described, which drives gear 44 mounted on the cylindrical protrusion 46 on the top plate 32. A wiper 48 is disposed between the gear 44 and the substrate 38 so as to be elastically encouraged into contact with gear 44, central contact area 40 and the resistive surface 42. The wiper 48 carries a plurality of wiping members 50 for contact with the conductive layer 42, three such wiping members being used in the preferred embodiment. The use of a plurality of wiping members assures electrical contact between the wiper 48 and the resistive layer 42 and prevents intermittant opens or noise in the event foreign matter is able to penetrate the potentiometer enclosure.

Now referring to FIGS. 3, 3a and 3b, further details of the construction of the potentiometer of FIG. 1 may be seen. Lead screw 52 slides into a mating opening in top member 32 and is retained therein by U-shaped member 54, which fits into a mating slot 56 in the top member 32. Slot 56 is located sufficiently close to the edge of top member 32 so that when the top member 32 is joined to base member 34, the edges of base member 34 partially close off slot 56 and entrap U shaped member 54 therein. A seal ring 58 is provided on the opposite end of the lead screw 52 to provide a restraint to the free rotation of the lead screw and to seal the potentiometer against ingress of foreign materials such as dirt, moisture etc.

Now referring to FIGS. 3a and 4, details of assembly of the base member 34 may be seen. The substrate 38 is a square substrate which fits within base member 34 and is cemented into position. Resistive layer 42 is in the form of a concentrically disposed circular arc and is electrically connected to conductive areas 60 and 62 which form the end connections for the potentiometer.

The central contact area 40, which is of the same material as the contact areas 60 and 62, also includes the contact area 64 extending from central contact area 40 to the edge of the substrate. The contact areas 60, 62 and 64 are electrically connected to the enlarged bases of terminals 24, 26 and 28, shown in phantom in the figure and located below the substrate 38, by gold ribbons 66, 68 and 70.

The central contact area 40, the end connections 60 and 62, and the connection 64 are formed by deposit ing a platinum gold paste to the substrate in a pattern and by firing the substrate to fuse the paste. The resistive layer 42 is formed in substantially the same way, being deposited in a circular arc, the ends of which overlap and make electrical contact with the end connections 60 and 62. Suitable pastes are readily available and may readily be deposited and baked in the desired manner by those skilled in the art of thick film processing. In the preferred embodiment, the resistive paste used to form the resistive layer 42 is a DuPont product sold under the name BIROX, and the platinum gold paste is also a DuPont product simply referred to as platinum gold conductive paste.

The substrate 38 is assembled into the base 34 of the potentiometer in the following manner. FIrst, gold ribbons 66, 68 and 70 are attached to the bases 36 of terminals 24, 26 and 28. This attachment may be either by welding the gold ribbons to the terminals or by cementing the ribbons to the terminals with a conductive cement, characteristically a silver epoxy, (that is an epoxy missed with powdered silver so as to be comprised of 90 percent silver). The substrate 38 is then cemented in position in the base 34 of the potentiometer, the ribbons folded over the top surface of the substrate as shown in FIG. 4, and attached to the appropriate conductive areas. If the silver epoxy is used to cement the gold ribbon to the terminals, the substrate 38 may be cemented into the base 34 as part of the same operation using only one cure cycle to cure the epoxy.

Now referring to FIG. 5, a perspective view of the wiper 48 may be seen. The wiper 48 is of uniform thickness and is characterized by a substantially circular area 72 having diametrically opposed tabs 74 created by slits 76 in the circular area 72. The tabs 74 have dimpled areas or depressions 78 near the outer edge of the tabs and projecting above the upper surface on the circular area 72. On one side of the circular area 72 is a downward curving member 80 carrying a downward projection dimpled area 82 colinearly disposed with respect to the hole 84 in the circular area 72. On the other side of circular area 72 is a downward curving member 86 which carries a plurality of wiping members 50 disposed so as to contact a plane which is substantially parallel to the circular area 72, in particular, the resistive area 42 is a substrate 38. The wiper members are adapted to contact resistive layer 42 along a radius thereof, and are formed by appropriate bends and cuts in downward curving member 80 to form individual and identical wiping members. The free separation of dimple 82 and wiping members 50 with respect to area 72 is slightly greater than the separation between gear 44 and the various layers on substrate 38. Consequently, in the assembly shown in FIG. 2, the wiper 48 is elastically compressed to insure contact by each of the plurality of wiping member 50 with the resistive layer 42, to assure adequate contact between dimple 82 and central contact area 40, and to retain gear 44 on cylindrical projection 46. In general, the wiper 48 should be fabricated from a precious metal to limit oxidation and for good conductivity. In the preferred embodiment, the wiper is a Paliney No. 7 material, a product of the Ney Metals Company.

The outer periphery of the surface 49 of gear 44, that is, the surface which mates with wiper 48, is serrated, defining tooth-like projections at a diameter equal to the diameter of depression 78 in the wiper 48. (FIGS. 2, 3a and 3 b) When the wiper 48 and gear 44 are assembled into a potentiometer as shown in FIG. 2, the depressions 78 engage the serrated portion of gear 44 so that gear 44 drives wiper 48 in rotation about the axis defined by cylindrical projection 46 and the dimple 82 in the wiper.

The top member 32 of the potentiometer has downward projecting stop member 90 (FIGS. 2, 3a and 3b) which projects into the area occupied by wiper 48. Downward curving member 80 of wiper 48 is disposed at a smaller radius than the downward curving portion 86 of the wiper so that member 80 is free to rotate about cylindrical projection 46 without engaging stop member 90. However, the downward curved portion 86 is disposed at a radius which will engage stop member 90. Thus, surface 92 of wiper 48 (FIG. 5) will contact stop member 90 at either extreme of the angular position of wiper 48 and the wiper will remain at that position upon further rotation of gear 44 because of the clutching action between the wiper and the gear. Stop member 90 is cooperatively disposed with respect to the wiper and substrate 38 so that wiping members 50 define an arc of travel extending from contact region 60 around resistive layer 42 to contact region 62, thereby limiting the travel of the wipers to something less than 360 and always maintaining the wipers within a region defined by the contact area 60 and 62 and the resisitive area 42.

Having now described the preferred embodiment of the present invention in detail, it may be seen that the construction of these potentiometers is extremely simple. The potentiometers of this embodiment have only six major parts, that is a top member, a base member, a coated ceramic member, a wiper and a gear. The only part of the assembly requiring individual attachment to another part of the assembly is substrate 38 and of course, the gold ribbons making electrical contact from the various films on the substrate to the terminal. .The remaining parts are simply placed in position in the assembly and the assembly put into the sonic welder for fusing the two potentiometer halves together. Thus, an exceedingly simple and reliable assembly is achieved. The top member 32, the base 34 and the gear 44 are Celenese X917, a product of the Celenese Plastics Co. and are molded to the finished dimension. Also, substrate 38 is generally cut from a larger substrate containing a plurality of patterns of resistive and conductive areas as required for the potentiometers, all formed in a single series of processing steps so that a plurality of resistive elements are simultaneously formed. Consequently, repeatable accuracy in the parts is assured and, because of the small number of parts involved in the assembly, there is a minimum opportunity for human error during the assembly.

Now referring to FIGS. 5, 6, and 7 a cross-section and a perspective view of an alternate embodiment of the present invention may be seen. In this embodiment the lower half of the potentiometer uses the same parts as the embodiment shown in FIGS. 1 and 2. The common parts in these two assemblies are the wiper 48, substrate 38 with the various films thereon and base 34 with terminals 24, 26 and 28 molded therein. The top portion of the potentiometer is comprised of a top member 81 having an integral stop member 83, a drive member 85 with a screw driver slot 87 therein for engagement by a screwdriver or other adjustment tool, and a sealing member 88 which provides both friction and sealing in response to the pressure on the sealing member resulting from the compression thereof by the slight interference fit of seal member 88, drive member 85 and dimpled area 82 with respect to central contact area 40 on substrate 38, induced by the elastic deflection of the wiper 48 in the assembly. The slot 87 does not extend over the full diameter of drive member 85. Thus, limiting the size of the tool inserted into the screw slot 87 in order to actuate the drive member 85, and more importantly to prevent damage to the cylindrical walls 91 on top member 81 by sharp edges by the tool used to adjust the potentiometer.

Drive member 85 has an integral cylindrical downward protruding member 92 which extends through a hold 94 in wiper 48 to provide a positive provision for mechanically driving the wiper by the driving member 85. In this regard, stop member 83 serves as a stop as did stop member in the embodiment of FIG. 2, but now the drive member 85 is also stopped, thereby indicating to the person making the adjustment that the end of the potentiometer wiper travel has been reached.

Now referring to FIG. 8, a perspective view showing some of the details of construction of a further alternate embodiment of the present invention, having a lead screw drive and side extending terminals, may be seen.

In this embodiment, base member has an upward extending edge 102 which is recessed on the top edge and back face to receive a terminal 104 which is sonically welded in place when base member 100 and top member are joined. Terminals 106 and 108 are molded into the base member 100 to provide the end connections to the potentiometer. This arrangement of the terminals disposes the inner ends thereof in cooperative relationship with respect to the contact areas 60, 62 and 64 on substrate 38, so that the required electrical connections therebetween may be readily made by silver epoxy cement 112. In all other respects, the details of this embodiment arethe same as the embodiment illustrated in FIGS. 1 through 5, and many of the same parts, such as substrate 38, wiper 48, lead screw 52, gear 44, seal ring 58, and U shaped member 54, are used in this embodiment. Such details having been previously illustrated and described in detail are omitted from FIG. 8 for purposes of clarity.

While the potentiometer of the present invention have been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

I claim:

1. A potentiometer comprising:

a lower section housing for receiving a resistance element;

a resistance element comprising a substrate having thereon a conductive region defining a central pad and a resistive region disposed in an arc substantially concentric to said central pad;

an upper section housing coupled to said lower section housing to form an enclosure, said housing having an elongated hollow portion for receiving an elongated screw and a downward projecting member for receiving a gear thereover;

a gear mounted on said downward projecting member, said gear and downward projecting member located substantially concentrically with said central pad;

an elongated screw located in said elongated hollow portion and meshingly engaging said gear;

a wiper of conductive material rotatably disposed over said downward projecting member, and adapted to be driven in rotation by said gear, said wiper having a first downward projecting extension with a depressed area thereon to form a rotatable contact with said central pad substantially concentric to said downward projecting member, and a second downward projecting extension with at least one wiping member thereon in slideable contact with said resistive region, the elastic compression of said wiper holding said wiper and said gear in functional disposition within said potentiometer.

2. The potentiometer of claim 1 wherein said wiper and said wiping member are integral members formed from a sheet of metal having a uniform thickness.

3. The potentiometer of claim 2 wherein said wiper has a plurality of wiping members, said wiping members being disposed in side by side relationship substantially along a radius of said resistive region.

4. The potentiometer of claim 1 further comprising a U-shaped member, said elongated screw having a c oncentric annular groove thereon, said upper section having an opening cooperatively disposed with respect to said lead screw; said U-shaped member being located in said opening and straddling said annular groove to axially retain said lead screw; and, said lower section entrapping said U-shaped member in said opening.

5. The potentiometer of claim 1 wherein, said gear has annular serrations on the lower face thereof, and

said wiper has at least one dimple cooperatively disposed with respect to said annular serrations for yieldably locking said wiper mechanism to said gear.

6. A potentiometer comprising:

a lower section housing for receiving a resistance element;

a resistance element comprising a substrate having thereon a conductive region defining a central pad, and an are shaped resistive region substantially concentric to said central pad;

an upper housing coupled to said lower section to form an enclosure, said housing having an opening in the top thereof; 7

a wiper drive member substantially coaxial with said central pad and having a drive means accessible through said opening in said upper member, said fe tfillilrifiin l uir fihit it lfil iriii i P a sealing means between said drive member and said upper member for retaining and sealing said last named members upon the urging of said drive member outward through said opening in said outward housing; wiper of conductive material rotatably disposed over said downward projecting member and adapted to be driven in rotation by said wiper drive member, said wiper having a first downward projecting extension with a depression thereon to form a rotatable contact with said central paid, said depression being disposed between said downwardly disposed projection and the upper surface of said central pad, so as to encourage said drive member outward through said opening in said outward housing, said wiper also having a second downward projecting extension with at least one wiping member thereon in slidable contact with said resistive region, the elastic compression of said wiper holding said wiping members in functional disposition with respect to said resistance element.

7. The potentiometer of claim 6 wherein said wiper and said wiping member are integral members formed from a sheet of metal having a uniform thickness.

8. A potentiometer of claim 7 wherein said wiper has a plurality of wiping members, said wiping members being disposed in side by side relationship substantially along a radius of said resistive region. 

1. A potentiometer comprising: a lower section housing for receiving a resistance element; a resistance element comprising a substrate having thereon a conductive region defining a central pad and a resistive region disposed in an arc substantially concentric to said central pad; an upper section housing coupled to said lower section housing to form an enclosure, said housing having an elongated hollow portion for receiving an elongated screw and a downward projecting member for receiving a gear thereover; a gear mounted on said downward projecting member, said gear and downward projecting member located substantially concentrically with said central pad; an elongated screw located in said elongated hollow portion and meshingly engaging said gear; a wiper of conductive material rotatably disposed over said downward projecting member, and adapted to be driven in rotation by said gear, said wiper having a first downward projecting extension with a depressed area thereon to form a rotatable contact with said central pad substantially concentric to said downward projecting member, and a second downward projecting extension with at least one wiping member thereon in slideable contact with said resistive region, the elastic compression of said wiper holding said wiper and said gear in functional disposition within said potentiometer.
 2. The potentiometer of claim 1 wherein said wiper and said wiping member are integral members formed from a sheet of metal having a uniform thickness.
 3. The potentiometer of claim 2 wherein said wiper has a plurality of wiping members, said wiping members being disposed in side by side relationship substantially along a radius of said resistive region.
 4. The potentiometer of claim 1 further comprising a U-shaped member, said elongated screw having a concentric annular groove thereon, said upper section having an opening cooperatively disposed with respect to said lead screw; said U-shaped member being located in said opening and straddling said annular groove to axially retain said lead screw; and, said lower section entrapping said U-shaped member in said opening.
 5. The potentiometer of claim 1 wherein, said gear has annular serrations on the lower face thereof, and said wiper has at least one dimple cooperatively disposed with respect to said annular serrations for yieldably locking said wiper mechanism to said gear.
 6. A potentiometer comprising: a lower section housing for receiving a resistance element; a resistance element comprising a substrate having thereon a conductive region defining a central pad, and an arc shaped resistive region substantially concentric to said central pad; an upper housing coupled to said lower section to form an enclosure, said housing having an opening in the top thereof; a wiper drive member substantially coaxial with said central pad and having a drive means accessible through said opening in said upper member, said drive member having a downwardly disposed projection defining a surface adjacent said central pad; a sealing means between said drive member and said upper member for retaining and sealing said last named members upon the urging of said drive member outward through said opening in said outward housing; a wiper of conductive material rotatably disposed over said downward projecting member and adapted to be driven in rotation by said wiper drive member, said wiper having a first downward projecting extension with a depression thereon to form a rotatable contact with said central paid, said depression being disposed between said downwardly disposed projection and the upper surface of said central pad, so as to encourage said drive member outward through said opening in said outward housing, said wiper also having a second downward projecting extension with at least one wiping member thereon in slidable contact with said resistive region, the elastic compression of said wiper holding said wiping members in functional disposition with respect to said resistance element.
 7. The potentiometer of claim 6 wherein said wiper and said wiping member are integral members formed from a sheet of metal having a uniform thickness.
 8. A potentiometer of claim 7 wherein said wiper has a plurality of wiping members, said wiping members being disposed in side by side relationship substantially along a radius of said resistive region. 